Use of remote-sensing technology for vehicle emissions monitoring and control

Measurement of exhaust emissions from vehicles during normal, on-road operation is key to any effective system for controlling air pollution in the transportation sector. It is essential to detecting discrepancies between certification-test performance and actual, “real-world” vehicle emissions, whatever the cause of the performance gap—equipment failure, normal deterioration with use, or deliberate efforts to cheat regulations. It offers a means of making certification-test protocols more robust and the results more in line with real-world performance. It gives regulators and researchers insight into both transportation’s contributions to local air-quality problems and the effectiveness of policies intended to mitigate those problems.

The most widely known method of in-use vehicle emissions testing employs a portable emissions measurement system, or PEMS. This involves sampling and analyzing tailpipe exhaust with equipment mounted on an individual vehicle as it is driven over the road or on a closed course, and produces a detailed, second-by-second record of emissions from that single vehicle. PEMS is widely used by researchers. It played a key part in detecting widespread evasion and cheating of vehicle emissions regulations by manufacturers, and has been incorporated into certification-test protocols for both heavy-duty and light-duty vehicles. But it is time consuming and expensive. And, while PEMS is less susceptible to cheating or gaming than a lab-based chassis-dynamometer test, it is possible for a modern vehicle to “know” that it’s being tested and react by changing the engine calibration and emission controls even with a PEMS setup. For these and other
reasons PEMS is not inherently well suited to fleet monitoring and surveillance.

Remote sensing as a means of measuring motor vehicle emissions is less well known, though it is a well-established research technique in that area as well as others, and like PEMS has been successfully deployed by vehicle emissions regulators. Compared to PEMS testing it is less expensive in terms of both time and money. That plus the unobtrusive (“remote”) nature of the technique make it well-suited to fleet monitoring. More generally, the basic characteristics of the data collected by the two methods—detailed second-by-second data on an individual vehicle or small number of selected vehicles from PEMS, one-second or half-second samples from a potentially very large number of vehicles from remote sensing—show them to be complementary tools that, deployed together, can produce a more precise and detailed understanding of not only pollutant emissions from on-road transport but also policy performance. 

This briefing is a concise introduction to the use of remote sensing in regulating and controlling pollution from on-road vehicles.